The present invention relates generally to a planar array type microwave antenna for use in receiving, for example, a satellite broadcast and more particularly, to a suspended line feed type planar antenna.
In the past, a suspended line feed type planar array antenna has been proposed in which a substrate is sandwiched between metal or metallized plastic plates having a number of spaced openings forming a part of radiation elements, constituting a circular polarized wave planar array antenna, in which a pair of excitation probes, which are perpendicular to each other, with a number of pairs which corresponds to the number of spaced openings, are formed on a common plane and the signals fed to the pair of excitation probes are mixed in phase within the suspended line (in our co-pending U.S. patent applications Ser. No. 888,117 filed on July 22, 1986 and Ser. No. 058,286 filed on June 4, 1987).
Thus, the above-mentioned planar antenna can be reduced in thickness and its mechanical configuration can be simplified. Further, though on inexpensive substrate available on t he market is employed for a high frequency use, an antenna gain equal to or larger than that of the planar antenna using an expensive microstrip line can be achieved.
The suspended line can achieve the advantages that it forms a low loss line for feeding the planar antenna, and also that it can be formed on an inexpensive film-shaped substrate, and so on. Further, since this conventional planar antenna utilizes a circular or rectangular wave-guide opening element as a radiation element, it is possible to construct an array antenna which has small gain deviation over a relatively wide frequency range.
Meanwhile, a so-called patch type microstrip line antenna has been proposed in order to reduce the thickness of the planar array antenna. Also, this patch type microstrip line antenna can be made high in efficiency and wide in band range by effective use of the advantages of the suspended line and the use of a thin radiation element, and it can be reduced in thickness and in weight at the same time, as is disclosed in our co-pending U.S. patent application Ser. No. 223,781 filed on July 25, 1988 and Ser. No. 258,728 filed on Oct. 7, 1988.
In a suspended line feed type planar array antenna in which a substrate is sandwiched between a pair of metal or metallized plastic plates, the resonance type printed patch radiators are formed on the substrate at positions corresponding to slots formed through one of the metal or metallized plastic plates thereby to form the planar antenna.
The thus formed antenna body is enclosed by a rear cover and a radome as shown in perspective view forming FIG. 1. Referring to FIG. 1, a bottom plate 2 made of metal or metallized plastic is located on a rear cover 1, and on the bottom plate 2, there is provided a film-shaped substrate 3 on which a number of resonance type printed patch radiators (antenna elements) are arranged. This film-shaped substrate 3 is sandwiched between the bottom plate 2 and a top plate 5 made of metal or metallized plastic having a number of spaced openings 4 corresponding to the respective antenna elements. The top plate 5, the film-shaped substrate S and the bottom plate 2 are fastened to the rear cover 1 by some suitable means such as screws or the like, though not shown. A support cushion 6 for supporting the radome 7 is provided on the top plate 5 which is then enclosed by the radome 7.
FIG. 2 is a fragmentary, cross-sectional view of the conventional planar antenna which is thus assembled to form a multi-layer structure.
In the above-mentioned conventional planar antenna, the rear cover 1 and the bottom plate 2 are formed independently, and also the radome 7 and the top plate 5 are formed independently so that the number of assembly parts is increased thereby, the structure thereof becomes complicated, the assembly-process thereof becomes sufficiently complicated as to degrade the productivity, the manufacturing cost is increased and the wight thereof is increased and so on.
Further, the top and bottom plates 2 and 5 and the substrate 3 must be secured to the rear cover 1 by using many screws, thus making the assembly-process cumbersome and degrading the productivity.